Tank,venting valves are usually driven at a particular pregiven pulse-duty factor. In the following, two switching states are referred to, namely, an open state and a closed state, which is to be understood as will now be explained. The closed state means that state wherein the valve is continuously closed. For tank-venting valves, this is, as a rule, the rest state. The open state is that state wherein the valve is driven by an opening signal at a pregiven pulse-duty factor such as at 10%, 50% or 90%. The term "open state" is therefore a generic term for many specific opening states at respective specific pulse-duty factors of the opening signal.
Tank-venting apparatus typically include the following components: a tank; an adsorption filter which is connected to the tank via a tank-venting line; and, a tank-venting valve which is connected into a connecting line which connects the adsorption filter to the intake pipe of an internal combustion engine.
The operability check of the tank-venting valve in its conventional configuration is based upon the fact that the tank-venting valve can be driven electrically. Values can be measured which are expected for the control current in dependence upon the control voltage. When these values are measured, the assumption can be made that the valve operates properly; otherwise, a fault is assumed.
It is common to check the operability of valves by monitoring the stroke of the actuating member of the valves. This can be performed mechanically, capacitively or inductively. An inductive check with the aid of a magnetic field as it is generated by a coil attached to an actuating member is especially effective. However, the configuration of such valves is very complex if the check of the operability is to be reliable, and the cost of such valves compared to those which cannot be checked as to operability is greatly increased.